1. Field of the Invention
The invention relates to a stator of an electric motor and, more particularly, to a split stator of an electric motor whose stator is formed by combining split stators.
2. Description of the Related Art
An example of split stators of an electric motor of this kind is a set of split stators that have a shape obtained by dividing a cylindrical stator in a circumferential direction, each split stator comprising a yoke portion that is divided in the circumferential direction, a tooth portion extending in a radial direction from the yoke portion, and a coil wound on the tooth portion, which is described in, for example, Japanese Patent Application Laid-Open Publication No. 2003-284269.
In the split stator described in Japanese Patent Application Laid-Open Publication No. 2003-284269, the coil is not covered with a cover. Therefore, when split stators are combined, there is a risk that the coils thereof may interfere with each other resulting in damage to the coating of the coil. In particular, the risk of interference and damage increase significantly when the coil is wound up on the outside of the coil housing portion in order to improve the coil density.
Furthermore, in this case, the interference between coils makes it difficult to bring the circumferential-direction end surfaces of yoke portions into contact, leading to a risk of failing to secure good circularity of the stator. In addition, if the circularity of the stator is not secured, the variations in the magnetic resistance of the yoke portions increase, greatly affecting the cogging torque (pulsating torque). Therefore, in order to avoid damaging the coil coating and secure good circularity of the stator, it is necessary to house the coil in the coil housing portion with an increased margin, by reducing the wire diameter of the coil, or reducing the number of loops of the coil, etc, thus resulting in a problem of failing to improve the coil density.